1. Field of the Invention
A method, and the apparatus to practice the method, used to drill multiple branch wells from a main generally vertical cased hole.
2. Description of the Prior Art
The invention described herein relates to work done by Maurer Engineering Inc. and Completion Technology Company under contract and subcontract, respectively, with the United States Department of the Interior, Bureau of Mines. Three other inventions also resulted from the work under this same contract. These are the copending patent applications entitled: "Method for Completing Horizontal Drain Holes," by Edward T. Wood et al bearing Ser. No. 276,609, filed Sept. 10, 1981; "Multiple Branch Well Containing One Producer and One Injector Well," by Edward T. Wood et al bearing Ser. No. 276,552, filed June 23, 1981, and "Multiple Branch Completion with Common Drilling and Casing Template," by Edward T. Wood et al bearing Ser. No. 276,551, filed June 23, 1981. There are also two related patents concerned with branch wells and in situ leach mining to wit: U.S. Pat. No. 4,222,611 entitled "In-Situ Leach Mining Method Using Branched Single Well for Input and Output," by W. C. Larson et al and U.S. Pat. No. 4,249,777 entitled "Method of In-Situ Leach Mining," by W. C. Larson et al.
The closest known invention to what is being disclosed and claimed herein is the cited patent application to Edward T. Wood (one of the coinventors herein) et al entitled "Multiple Branch Completion with Common Drilling and Casing Template" (hereinafter referred to as the closest invention). Its contents are specifically incorporated by reference herein. As indicated therein, the contents of that and this invention was first made available to the public in an ASME publication 81-PET-2 entitled "Drilling and Completing Multiple Branched Boreholes for In Situ Leach Mining" distributed on Jan. 18-22, 1981.
The essential similarities between this invention and the invention referred to as being closest can be found in several aspects. Each is concerned with a method of forming multiple branch wells from a main generally vertical cased hole for primary use with in situ leach mining. And each employs whipstocks and a drilling template which engages an indexing dog to properly orient the drilling assembly with respect to the main casing to allow drilling of the branch wells. There are also several important differences between these same two inventions. In this invention, the main casing has at least one easily-penetrated exit points or windows, in its side, corresponding to the beginning point for at least one of the multiple branches to be constructed. Herein there is both a drilling template and a tubing template which are engaged by the indexing dog to orient the drilling assembly or casing tubes, respectively. Further, in this invention, the templates are mounted vertically to form and engage at least one of the branch wells that are formed through the main casing. None of these features are present in the closest invention. As a result, this invention allows a smaller main casing (95/8" O.D.) to be used with three smaller branch casings (each of 3" O.D.). This in turn means less cost to set up the well system for production in a shorter time.